1. Field of the Invention
The present invention relates to a picture quality improving apparatus for providing excellent color reproduction and a more subjectively pleasing white on an image of a color television receiver.
2. Description of the Prior Art
In the present day color television receiver, very annoying noise disturbances appear in a high-saturation color portion of a picture such as a saturated red or a saturated blue. In addition to the noise disturbances, the saturated color portions suffer from decreased sharpness and luminance errors. The decreased sharpness gives viewers the same effect as so-called "blooming", which is a lack of sharpness in highlight portions of a picture. The luminance errors are perceived by viewers as extreme enhancements of colors.
As described in the U.S. Pat. No. 3,835,243 the invention of which was made by one of the present inventors, these unwanted disturbances come mainly from the higher correlated color temperature of reference white of a modern color television receiver. It has been made clear that these disturbances can be minimized by optimum design of chrominance demodulators or making the correlated color temperature of reference white rather low such as CIE Illuminant C (6774K) or D65 (6500K). In the United States of America, increasing numbers of TV manufacturers have adopted the lower correlated color temperature for the above reasons. Although the lower color temperature provides excellent reproduction of chromatic colors (fleshtone, red, blue etc.), achromatic colors such as white are made rather nonattractive or not pleasing, as compared with the higher color temperature, because of human preferences. Under existing technology, TV designers must choose one of two alternatives: vivid chromatic colors or clear and pleasing achromatic colors. No means have yet been found which make it possible to reproduce vivid and clear chromatic and achromatic colors simultaneously.